Electrophotographic developer electrode



Jan. 11, 1966 w. SIMM ETAL 3,228,608

ELECTROPHOTOGRAPHIC DEVELOPER ELECTRODE Filed June 11, 1963 2Sheets-Sheet 1 F/GJ INVENTORS W4LTER S/MM BY OTTO KOC Jan. 11, 1966 w.SIMM ETAL ELECTROPHOTOGRAPHIC DEVELOPER ELECTRODE 2 Sheets-Sheet 2 FiledJune 11, 1963 mmm ww m xmw Du Dn E0 m 0 m United States Patent 3,228,608ELECTROPHOTOGRAPHIC DEVELOPER ELECTRODE Walter Simm, Opladen, and OttoKoch, Cologne-Stammhelm, Germany, assignors to Agfa Aktiengesellschaft,

Leverkusen, Germany, a corporation of Germany Filed June 11, 1963, Ser.No. 287,041 Claims priority, application Germany, June 29, 1962, F37,187; Dec. 20, 1962, F 38,613 1 Claim. (Cl. 23915) This inventionrelates to an electrophotographic developer electrode forelectrostatically atomizing the electrophotographic developer liquidwhich is characterized by a hollow cylinder, which widens out at thebottom in the form of a funnel with a sharp edge and a reflux tube beingarranged inside the hollow cylinder for transporting back the excess ofdeveloper liquid, whereby the opening of the reflux tube lies near thefunnel shaped outlet of the hollow cylinder.

In the Belgian Patent 616,914 is described an electrophotographicdeveloper apparatus which is characterised by the combination of anelectrostatic atomiser electrode consisting of hollow cylinder whichwides out at the bottom in the form of a funnel and has a sharp edge,with a grid electrode.

This atomiser electrode has various disadvantages. Thus, for example,the mechanism for adapting the velocity of the pump which controls therate of supply of developer fluid, to the desired atomising conditionsis very susceptible to trouble and requires additional expenditure dueto the use of adjustable gearings for the supply pump. If the apparatusis out of action for any length of time, the electrode very easily driesup so that it first has to to be cleaned, filled and wetted before itcan be used again. Even slight leakages in the punmp of faults in theoutlet aperture of the electrode disturb the equilibrium between thequantity of fluid supplied and the quantity of fluid used up byatomisation in the atomiser funnel so that uniform atomisation of fluidis then no longer possible. In such cases, large drops are frequentlyfonrned and corona discharges occur. When using concentrated colourdeveloper solutions, a sludge is easily formed in the electrode funneldue to evaporation of solvent, and this may cause the tubes of theapparatus to get blocked.

We now have found that these disadvantages may be overcome by means of areturn flow tube arranged inside the hollow cylindrical atomiserelectrode described above. In such an arrangement, the liquid is carriedin a cycle from the tank to the opening of the electrode and from thisopening back into the tank. The edge of the electrode is continuouslywetted, but the liquid does not drip out even when no voltage isapplied.

The atomiser electrode according to the invention is showndiagrammatically in the accompanying drawings: FIGURE 1 shows oneembodiment, in which the developer liquid is transported by means ofpumps.

The hollow cylinder 1 with the tunnel shaped end 2 is provided with areturn flow tube 3 which is inserted in the cylindrical part thereof andcan be moved longitudinally. Between this tube and the wall of thecylinder there remains a space 4 through which the liquid which is to beatomised and which enters through a lateral filling tube 5, can descendunimpeded into the funnel-shaped portion 2 of the electrode. The bottomopen end of the inner tube 3 lies in the bottom end respectively in thefunnel shaped part of the cylinder but does not project beyond it. Atthe top end, the gap between the tube 3 and the wall of the cylinder istightly sealed with the exception of the inlet through which the liquidenters. The filling tube 5 and the tube 3 communicate with pumps 6 and 7respectively or with two separate chambers 6, 7

3,228,608 Patented Jan. 11, 1966 of a pump, such as a geared pump. Theconnections are so arranged that the pump or pumps are in operation, theliquid is sucked from a tank 8 and delivered to the inlet 5 while theliquid, sometimes with a small portion of air, is sucked at the same orslightly greater pump output from the tube 3 and returned to the tank 8.

At the beginning, when the pumps are already in operation but theelectrode is not yet filled with liquid, the liquid first flows down inthe gap between the tube 3 and the cylinder 1 to the edge of the funnel.However, the space inside the funnel fills only down to the level atwhich the liquid surface below the bottom opening of the inner tubecloses. At that moment, suflicient liquid is immediately sucked olfthrough this opening so that there is no further change in the level ofthe liquid, so that no drops will be formed at the bottom end of theelectrode. The amount of liquid contained in the electrode when a steadystage has been reached may be varied by varying the immersion depth ofthe inner tube so that the lower portion of the electrode may be filledwith liquid more or less to the edge.

The tunnel shaped extension 2 is not absolutely necessary for regulatingthe liquid as described above. The lower end of the electrode could becylindrical but has been designed to expand merely because this improvesthe atomising conditions.

The atomiser electrode according to the invention has the followingadvantages:

The pump output may be fixed once and for all to a certain valueindependently of the physical properties of the liquid, the voltage andthe distance between the electrodes. The pump output need not bemaintained exactly at this value but may be allowed to fluctuate withinrelatively wide limits so that it is possible to use very simple pumps.The rate of liquid supply may be considerably greater than the rate atwhich the liquid is atomised, so that the reserve liquid can be mixedthoroughly. In this connection, a further advantage of the invention isthat the pump assembly can be kept in oper ation continuously even whenno aerosol is produced. Atomisation is then regulated merely byswitching the voltages on and off. One great advantage of the electrodeconsists in that the apparatus is ready for use almost immediately afterit is switched on even if the pumps have been out of operation for sometime and the nozzle is dry, because the return flow system ensureswetting of the apparatus and maintains the liquid in the electrode atthe normal level.

FIGURES 2 and 3 show another embodiment of the developer apparatusaccording to the invention. When the embodiment according to FIGURE 1 isused for developing pictures on a continuous paper strip, it has beenfound inconvenient for the electrode to be connected to a pump and tothe liquid tank through an inlet tube and a reflux tube. This isparticularly inconvenient when the electrode has to be moved or severalelectrodes have to be used simultaneously. Another disad vantage of theatomiser electrode is that the liquid sprayed from the electrode is notdeposited evenly on the opposite electrode but at greater density atcertain areas owing to the liquid cones forming at the edge of thespray. The said disadvantages are overcome by using a developerelectrode with a conveyor worm in the space between the reflux tube andthe wall of the hollow cylinder. The electrode then consists of theknown hollow cylinder 1 which widens at one end in the form of asharp-edged funnel 2 and which contains a reflux tube 3, the importantimprovement being effected by arranging a conveyor worm 9 between thereflux tube and the cylinder wall, this worm taking up a portion of thewhole length, e.g. /s of the length of the electrode. The electrode maybe arranged vertically or obliquely and FIGURE 3).

the sprayedge 2 is positioned at the top end of the cylinder. Theconveyor worm is advantageously rigidly connected to the reflux tube andis situated in the lower part of the cylinder so that the liquid cycle,to be described in more detail below, provides a tight liquid seal inthe-upper part and as little air as possible is mixed with the liquid.The hollow cylinder with the reflux tube and the conveyor Worm extenddirectly into the tank and the lower part of the cylinder is immersed inliquid. The hollow cylinder is mounted to be rotatable aboutitslongitudinal axis at the point where it enters the tank. The refluxtube is rigidly fixed to the bottom of the tank and outlets 11 for-thereturning liquid are provided at the lower end of the reflux tube. Theedge of the hollow cylinder, which is immersed in liquid, is situatedjust above these apertures and must not cover them, because, when theapparatus is in operation, air is carried with the returning liquid andthis air must be allowed to escape and not be carried into the liquidcycle as otherwise froth is formed which interfered with the operationof the apparatus.

In this arrangement, it is easy to rotate the cylinder -by-means of anexternal drive, eg, a worm wheel 12 and a worm 13, whereby the liquid israised from the tank owing to the relative movement between the cylinderwall and the conveyor worm 9, so thatthe liquid can be conveyed to theupper edge of the electrode. When the liquid reaches the --t-op end ofthe electrode, it we-ts the spray edge 2 and returns to the tank throughthe reflux tube 3. The liquid-is kept constantly stirred in this cycleso that no deposits will be formed from highly concentrated dyestuffsolutions. This rotation of the cylinder not only ensures that the sprayedges -will be kept wetted but also ensures uniform distribution anddeposition of'the' aerosol because there are no preferred spraydirections as is the case witha stationary spray edge. When theelectrode is not in operation, the liquid returns to the tank so thatallparts of the electrode are emptied.

Owing to the space saving arrangement of the electrode, the conveyorworm'and the tank, the atomisation may=easily be intensified byconnecting several electrodes to a common tank and driving themsimultaneously (see In this arrangement, it is advantageous to impart.periodic reciprocal movement to the tank and the electrodes, asthisimproves the distribution of aerosol. 'For this purpose, the drive shaft14 must be connected to the drive motor lfi'through a sliding clutch 15so that the motor will 'not take'part in this movement. The atomiserapparatus may be increased'to any degree of complexity by the provisionof any number of electrodes in the manner described above.

The following dimensions are given by way of example for the atomiserelectrode according to the invention:

length of cylindrical part, a, to 100 mm. Diameter of the cylindricalpart, b, 3 to 6 mm., preferably 4 mm. Internal diameter of thecylindrical part, c, 2.5 to 5-mm.,

preferably 3 mm.

Diameter of the tube 3, d, 0.5 to 4 mm., preferably 2 mm.

Internal diameter of the tube 3, e, 0.3 to 3 mm., preferably 1 mm.

Diameter of the edge of the funnel, f, 1 to 10 mm., preferably 6 mm.

Cone angle of the funnel, g, 20 to 100, preferably The pump output mustbe sufficient to ensure that atomisation of liquid will not beinterrupted due to shortage of liquid. However, the output may be amultiple of the minimum output, e.g., 1 cc. per min. when the rate ofatomisation is 0.2 cc./min. The best position for the electrode when inoperation is with its longitudinal axis in the vertical positionalthough it may also be inclined.

Atomisation may also be carried out with the electrode rotated through180 so that the outlet is directed upwards. In that case, the aerosol ispreferably sprayed upwardly.

The processing of .the electrophotographic materials up to the stage ofdevelopment may be carried out in known manner, for example, asdescribed in Belgian Patent 616,914.

Many different types of electrophotographic materials may be processedin this apparatus, for example, those described in German patentspecifications 1,090,093; 1,046,493; 1,031,127 and 1,052,811.Particularly suitable are the usual electrophotographic materials whichcontain 'Zll'lC oxide, dispersed in an insulating binding 3 agent, asthe photoconductive substance. 'Suitable developer solutionsaredescribed in Belgian Patent 616,914.

We claim:

An electrophot-ographic developer electrode for electrostaticallyatomizing the electrophotographic developer liquid comprising a hollowcylinder which is widened at its bottom end in the form of a funnel witha sharp edge, a reflux tube disposed within said hollow cylinder fortransporting back the excess of developer liquid, said reflux tube beingopen at its lower end near the funnel shaped outlet of said hollowcylinder, an inlet aperture in the upper end of said hollow cylinder forthe admission of the liquid, an outlet aperture in the upper end of saidreflux tube, and pump assembly means being connected to said inletaperture of said hollow cylinder and 'to said outlet aperture of saidreflux tube whereby the liquid sucked .from atank may be introduced intosaid electrode through said inlet aperture of said hollow cylinder andreturned to the tank through said outlet aperture of said reflux tube.

M. HENSON WOOD, JR., Primary Examiner.

EVERETT W. KIRBY, Examiner.

